Process of producing sheet metal



May 2, 1933. J. B. TYTUS EROQESS OF PRODUCING SHEEIMEI'AL Filed Jan. 18 1929 2 Sheets-Sheet. 1

I N VEN TOR.

ATTORNEYS May 2, 1933.,

J. B. TYTUS PROCESS OF PRODUCING SHEET METAL Filed Jan. 18, 1929 '2 Sheets-Sheet 2 INVENTOR- WM 5. 7% BY 2 W .4 TTORNEYS i of strips into sheet metal of the proper gauges pickling,

Patented May 2, 1933 UNITED STATES.

PATENT OFFICE JOHN B. T178, 0] II'DDLETOWN, OHIO, ASSIGNOR TO THE AMERICAN BOLLIIlG- HILL OOIPANY, O! mnnm'own, OHIO, A. CORPORATION OF OHIO PROCESS OF PRODUCING SHEET METAL hpplieation flled January 18, 1929. Serial No. 838,268.

My invention has to do with the so-called continuous methods of producing wide stri in the manufacture of sheet iron and stee These methods may involve as an example, the rolling of ingots into slabs, the hot-rolling of slabs into strips, and the cold rolling for shearing into sheets of commercial form.

Continuous and discontinuous heat treatprimarily is directed to the production of new sheets having properties hitherto unattainable in the processes as practised. I In order that my invention may be understood, it is necessary to point out some problems in the continuous processing of sheet metal which are solved by my invention. As an exam 1e of a process in present use, strip is made y a method comprising hot rolling,

cold-rolling to gauge, box annealing in coils, and skin passlng if desired. As a substitute for box annealing, or as an extra step in the process, a continuous annealing may be used. Such continuous annealing may comprise passing strip or stitched sheets through a furnace of horizontal type maintained at a suitable temperature for annealing, and of such length taken together with the rate of travel of the material therethrough as will allow the pro er time interval for the heat treatment. uch furnaces will be understood as equipped with the necessary cooling ducts and the like for the satisfactory handling of sheet metal.

The first difiiculty arises inthe lack of uniformity of the hot-rolled strip. With a given batch of metal, if the temperature of the slabs being rolled were always uniform the rolling be done with stock always well above the A3 point at the end of the rolling suchannealed stock it is strained beyond its elastic-11mm in many places, these strained areas being known as cross breaks or coiler breaks. In difiicult drawing operations these cross breaks again become evident as welts across the drawn pieces, even though the sheet process has proceeded with additional cold-rolling and box annealing. Obviously also the same difiiculty resides in the mere annealing of the sheet subsequent to all cold-rolling to gauge.

Again, since annealing involves considerations of time, temperature, atmosphere and the like, and since continuous annealing operations are limited by the apparatus employed and the commercial considerations of speed of travel, further difficulties arise. Box annealing is thus far the most carefully controlled type of annealing and gives best results. It has already been pointed out why it is unsuitable for intervening annealings in a cold rolling process of continuous character. Hence such intervening heat treatments as may be necessary have usually been of the continuous type, and box annealing is preferably carried on with the strip cut apart in sheets and placed in the boxes in packs. But while in box annealing the general conditions of time, temperature and atmosphere may be most carefully controlled, there is a limit upon the temperatures practicable, and further there is a lack of absolute uniformity in the heat treatment in any given box, because it is not possible to heat perature under identical conditions.

However, non-uniformity persists through all of these annealing treatments, whether continuou or box. Broadly it is not possible to produce metal of absolute uniformity so far as strains are concerned arising from revious working, excepting the metal be heated above the A3 point, or into the lower part of the gamma range. This cannot be done in ordinary box annealing processes. In other words, in commercial practice, it is got practicable to attempt to'norngilize in a My process, briefly stated, comprises the following steps; hot-rolling, pickling, coldrolling to gauge, normalizing, picklin shearing, box-annealing, and if desired, skln passing, leveling or the like subsequent cold rolling operations.

By this process I am able to make continuously sheets of great uniformity as between individual pieces. My sheets are characterized by a fine and uniform grain, are ractically free from non-uniformit of p ysical properties in the piece, and s ow no evidence of directional properties. The are practically free from any tendency to cross breaks. They have the further advantage that they may be produced continuously and rapidly with the attendant commercial savmgs. I

They are the equivalent of the best deep drawing sheets hitherto produced by any process; and they are superior in properties to sheets hitherto produced in continuous processes. The exact reasons why this is so involve matters of structure and grain condition upon which I do not wish to be bound by theory. A long series of experiments and tests have demonstrated the fact that my process produces a superior deep drawing product.

The objects of my invention set forth 'above, and others which will be set forth hereinafter or will be obvious from what follows, I accomplish by that certain process of which I shall now'describe a preferred embodiment, reference being had to the 'drawings accompanying these specifications.

In the drawings Figures 1 and 2 show diagrammatically and in sequence the steps of my process, and are to be taken together.

In Figure l, a slab #1 which may be cold, is' heated to a tem erature for hot rolling in a billet heating urnace 2, usually of the pusher type. The hot slab may then be passed through a universal mill 3 with edging passes, and then through a tandem of four four-high hot mills 4, 4a etc. It is now in the form of a hot-rolled strip which is coiled on a coiler 5 into the coil 6. The coil 6, at the start of the next step, is placed in an uncoiler 7. As additional coils are processed the ends thereof may be connected together by a traveling spot welder 8 or otherwisefso that to all intents and purposes a continuous traveling strip of metal is formed for further processing. Thisstri which I have now indicated as 9 passes t rough a continuous picklin tank 10 which may be equipped with scru her and dryin furnace, indicated broadly as 11,'and is t en after having been sheared a art into strips again by a shear 12, recoile into a coil 6a by a coiler 13.

When ready for the next step, the coil 6a is uncoiled n an uncoiler 14. The next step is a cold rolling to gauge, and is to be distinguished from mere skin passing, or rolling for leveling and the like. It is such a cold rolling as results in a substantial reduction of the metal, and is relied upon to produce substantially the required finished gauge.

It may be accomplished by a tandem of four or more four-high cold rolls, indicated at 15, 15a etc. The operation is usually finished by a recoiling into coils 61) on a recoiler 16.

Next, an uncoiler 17 straightens out the coil 66, and again a traveling spot welder 18, a stitcher, or other suitable device connects the strips serially for continuous processing. The band of metal is conducted through the heat treating furnace 19 which will be preferabl fitted with a cooling duct 20. A norma izing process is carried on in this furnace, and I desire it to be understood that by this term I mean such a heat treatment as will bring the metal above the A3 point, or into the lower part of the gamma range followed by a quick cooling, as distinguished from a mere annealing. By doing this I recrystallize the entire sheet or strip with a fine, uniform grain. In other words, at this point I bring out such a rearrangement of the structure of the metal that all strains of whatever character hitherto produced in it are wiped out as though they had never been. Such a rearrangement is a thing which occurs naturally when the normalizing temperature is reached. For the normalizing of steel or iron of any given carbon content the necessary temperature may quickly be found in the well known iron-carbon equilibrium dia ram for the critical range.

0 far as I am aware continuous furnaces have not hitherto been used for heat treating operations above the A3 point, i. e. for normalizing cold reduced material when the cold reduction has been of the order of 20% or higher. Yet the continuous furnace is well adapted for normalizing. Ordinary annealing is a function of time and temperature, as well as other conditions, and as has already been pointed out the control of all of these conditions is difiicult in continuous operation. No such difiiculty however attends continuous normalizing, and it is only necessary to raise'the furnace temperature lid eonora to such a point as to cause the sheet with certainty to reach the A3 point to accomplish this end. The time of the treatment is unimportant providing the temperatureis attained, the change occurring at the temperature, and indeed it is a thing which may be controlled by visual examination, if desired. The sheet or strip is normalized when the dark spots disappear. The operatingadvantages of continuous normalizing over continuous annealing will be obvious.

After the normalizing, the strip is conducted through a pickler 21, scrubbers and drying furnace, indicated at 22 may again be used, and the strip is sheared by a shear 23 into sheets 2%. The next step in my process is a true annealing, which may be carried on by placing packs of the sheets 24 into boxes 25 and heating these in a furnace 26. Afterwards the sheets may be given a skin passing in mill 27'to level them, finish their surfaces and fit them for deep drawing op- 'erations. The finished product is indicated in the diagram at 28.

T have hitherto distinguished normalizing from annealing below the A3 point, and have indicated that particularly for continuous processing normalizing has distinct operating advantages because of the quick cooling.

I have described in this specification a process involving in sequence normalizing and .annealing. While not commercially practicable, it is possible to' carry the temperature in annealing, tov a point above A3. This might even be done in a box. But it would neither result in normalizing nor in the effects of a combination of normalizing and subsequent annealing. This is because of the grain growth incident to the necessarily slow cooling down throughthe A3 point. Normalizing and then annealing below the A3 point pro Vides a way of eliminating strains and correcting the microstructure of iron or steel while dropping out of the process the dis-' advantageous slow cooling through the dangerous or critical temperature ranges. The A3 point referred to isa thermal critical point varying for diiferent carbon contents.

it is discussed on page 530 of the Making, I

- an example, instead of carrying my process through with strip, I may use sheets, which will preferably be connected together by stitching fol-the continuous parts thereof. Or again, each step of my process may, if desired,'and at some sacrifice of economy, be carried on discontinuously. Various modifications may be practised without departing from the spirit of my invention, or varying that sequence of process steps with which a my invention is concerned. Having thus described my process, what I claim as new and gauge by hot and cold rolling, and before annealing subjecting said metal to a normalizing heat treatment whereby strains due to Working are completely removed, and afterwards annealing said metal. I

i. That process of producing sheet metal which comprises the ste of cold rolling to gauge, normalizing, pic ling and annealing.

5 That process of producing sheet metal which comprises the steps of cold-rolling to gauge, continuously normalizing, continuously pickling, shearing and box annealing.

6. Thatprocess of producing sheet metal which comprises hot rolling slabs to form strips, interconnecting said strips and pickling them, shearing into strips, cold-rolling said strips to gauge, interconnecting said strlps and continuously normalizing and pickling them, shearing said strips into sheets and box-annealing said sheets in packs.

l. That process of producing sheet metal which comprises hot-rolling, pickling, coldrollmg to gauge, normalizing, pickling, shearing to sheet length, box annealing and surface finishing.

8. That process of producing iron or steel sheets of a carbon content less than .25 which comprises cold-rolling metal of said character to gauge, and prior to an annealing treatment, heating said metal to 1650 degrees F., quickly cooling and afterwards annealing said metal.

9. That process of producing iron or steel sheets of a carbon content less than .25 which comprises hot rolling metal of said character, pickling, cold-rolling said metal to gauge, heating said metal to 1650 degrees F, quickly cooling said metal, pickling, shearing said metal to sheet length, box annealing the sheets so formed, and skin passing said sheets.

JOHN B. TYTUS. 

